The present invention relates, in general, to tape automated bonding lead frames, and more particularly to a tape automated bonding lead frame which provides for multiple power and ground planes located in a single plane, arranged concentrically about an integrated circuit bonded to the lead frame.
With a steady increase in the number and density of leads required for semiconductor devices, tape automated bonding (TAB) has become the technology of choice for many high density applications. Among the problems to be overcome as leads become more and more densely packed are those related to capacitive coupling and lead impedance. In the past, these problems were addressed by the addition of a ground plane located parallel to, but electrically isolated from the plane of the TAB leads. In many applications, however, it was necessary to isolate high current ground lines connected to devices which were switching on and off from low current ground lines which showed less fluctuation in current levels. Failure to make such an isolation could, for instance, introduce noise from a power output back into a signal input, yielding an unacceptable signal to noise ratio.
Multiple power and ground planes represented an expensive solution to the problem. Dividing a single ground plane into radial sections was an effective approach in many ways, but also had some shortcomings. First, the electrical field which each lead saw was different, depending upon the potential on the nearest power/ground plane segment. Thus the shielding each lead saw was different. Also, in many applications multiple connections to the same power or ground potential were required, but were not co-located upon the semiconductor device. The same ground potential was required on two or more different sides of the semiconductor device. Multiple connections to a single power potential were likewise required. Such connections were not always easily made with the radially segmented ground plane.